The invention relates to optical systems containing gradient index lenses.
Optical images may be transferred by means of a lens system employing, e.g., standard objective and relay lens sections or, in other applications, relay lenses alone. In applications where size is critical, e.g. in endoscopes for viewing within the body, e.g. in a joint, through a puncture wound without extensive surgical opening, a small-sized, e.g. 1 to 3 mm diameter, cylindrical rod lens system with radial index distribution (GRIN lens) may be substituted.
GRIN objective lenses currently available limit the field of view of the endoscope to less than is desired. Attempts to increase the field of view of the GRIN objective lens are limited by the glass chemistry of the lens material. Also, the field of view of the GRIN objective lens is decreased when it is necessary to use a line-of-sight prism attached to the endoscope. To increase the field of view, a homogeneous lens typically is affixed to the endoscope, however, the addition of this homogeneous lens changes the relative positions of the aperture stop and the field stop resulting in reduction of the optical invariant and thus the light throughput of the system.
The usual method of correcting for the decrease of the light throughput is to increase the diameter of the optical elements. However, in many applications, e.g., endoscopes, it is desirable that the diameter of the system be maintained at a minimum.